1. Field of the Invention
The present invention relates to a driving device and an image forming apparatus, and in particular to a positioning mechanism that positions a rotating shaft on an input side and a rotating shaft on an output side in a deceleration mechanism used for a transmission path of driving force.
2. Description of the Related Art
As is well known, in an image forming apparatus, such as a copying machine, a printer, and a printing machine, an electrostatic latent image formed on a photosensitive drum serving as a latent image carrier is developed into a visible image with developer supplied from a developing unit. The image thus developed into the visible image is transferred and fixed onto a recording sheet or the like, whereby a copy output operation is performed.
The latent image carrier is a member used for forming an image with a plurality of colors as well as a single color. When images of a plurality of colors are superimposed, for example, by a tandem electrophotographic process in which a plurality of latent image carriers are arranged along the moving direction of a transfer body, operational timings for forming the images of the colors need to be matched.
The operational timings not being matched cause an abnormal image such as color deviation.
Conventionally, a mechanism that drives a latent image carrier is configured to cause a deceleration mechanism to decelerate driving force of a driving motor and to transmit the driving force to the latent image carrier. An example of the mechanism include a configuration in which a planetary gear mechanism whose input shaft is an output shaft of a driving motor is used as a deceleration mechanism (for example, Japanese Patent No. 4360162).
Japanese Patent No. 4360162 discloses the following structure.
Specifically, FIG. 12 is a schematic of a structure disclosed in Japanese Patent No. 4360162. In FIG. 12, an output shaft D is provided to a carrier C that rotates while supporting a plurality of planetary gears P that revolve around a sun gear S supported by an output shaft M1 of a driving motor M. The output shaft D is rotatably supported by a shaft bearing U fixed to a decelerator case K that houses therein the planetary gear mechanism. In this structure, the output shaft of the driving motor M corresponds to a rotating shaft on the input side, and the output shaft D provided to the carrier C corresponds to a rotating shaft on the output side. In FIG. 12, K1 denotes internal teeth engaged with the planetary gears P arranged on the inner surface of the decelerator case.
A latent image carrier is a member that needs to be replaced when its photosensitive layer deteriorates over time.
Conventionally, so as to make a latent image carrier replaceable, a structure in which an output shaft of such a deceleration mechanism disclosed in Japanese Patent No. 4360162 is coupled to a photosensitive drum via a coupling to make the photosensitive drum detachable has been developed (for example, Japanese Patent Application Laid-open No. 2001-200858).
As for structures embodying the engaging relationship between the output shaft integrated with the carrier of the deceleration mechanism and the latent image carrier, Japanese Patent No. 4360162 employs the structure in which the output shaft itself is extended to be supported by the latent image carrier, and Japanese Patent Application Laid-open No. 2001-200858 employs the structure in which the output shaft is coupled to the shaft of the latent image carrier via the coupling.
In both structures, however, the length of the output shaft is made large, resulting in an increase in the space occupied by the deceleration mechanism adjacent to the latent image carrier.
To address this problem, a structure in which a deceleration mechanism is housed in a latent image carrier, and a driving motor is arranged outside of the latent image carrier has been developed (for example, Japanese Patent Application Laid-open No. 2004-219836). With this structure, the space occupied by the deceleration mechanism in the axial direction of the output shaft extending from the driving motor to the latent image carrier can be made small.
In each of the structures disclosed in Japanese Patent No. 4360162, Japanese Patent Application Laid-open No. 2001-200858, and Japanese Patent Application Laid-open No. 2004-219836, because the output shaft of the deceleration mechanism that houses the gears in the housing is used as the drive shaft of the latent image carrier, the deceleration mechanism needs to be connected precisely to the latent image carrier. As a result, the yield of processing the deceleration mechanism remains low, thereby increasing the operating cost and parts management cost.
By contrast, in the driving device itself using the deceleration mechanism, the structure of the output shaft is changed depending on the size of the latent image carrier to be used. The part management for the deceleration mechanism itself that houses the gears in the housing is required in accordance with changes in specifications, whereby the management cost may be increased. In addition, for the maintenance of the deceleration mechanism, the deceleration mechanism itself attached to the driving unit of the latent image carrier needs to be removed. As a result, operations required for the maintenance are made complicated.